1. Field of the Invention
The present invention relates to a method and device for detecting, locating and characterizing differences in density, structure or chemical composition of a biological tissue.
2. Description of the Related Art
In the prior art various methods have been put forward for detecting or evidencing tissue differences of physiological or histological origin, whether pathological or not, using the auto-fluorescence of tissues containing endogenous chromophores or the fluorescence caused by administered dyes or exogenous chromophores.
This made it possible to achieve real time mapping of the fluorescence of living tissues, based on the principle according to which the chromophore content differs depending on whether the observed area is healthy or damaged.
Said method has been used for the direct observation of decay damage on hard tissues such as tooth enamel, or on soft tissues such as the skin or oral mucosa, or via endoscopic route for observing thoracic or gastric endocavity mucosa.
Various methods have also been proposed for detecting and characterizing tissue differences in which the tissues are illuminated by means of a monochromatic light of determined wavelength so as cause this light to feed back radiation by luminescence at a different wavelength.
According to this principle, and as an example, by comparing the intensity of the luminescence emitted by a healthy area of a tooth and a decayed area thereof, using respective measurements in these two specific wavelengths, in particular using a mathematical operation to calculate the difference between these two intensities, it is possible to determine the presence of decay or to evidence tissue difference or surface deterioration in relation to the value obtained.
Said method has also been used for the in vivo detection of inflammatory processes of the pancreas in animal models in which significant tissue discrimination was obtained between healthy tissues and damaged tissues by comparing the spectra and intensity ratios between the blue and red.
In the literature other applications are found, in particular for the in vivo detection of cancers of the tracheal-bronchial structure, for which it was found that the auto-fluorescence of the bronchi is modified when the tissue changes from a dysplastic state to a carcinomatous state. In this case it was found that the lesions led to reduced green fluorescence at around 500 nm and to an increase in the red spectrum band at around 600 nm.
This same principle is also used in ophthalmology to asses the extent of transparency of the lens whose photo-oxidized proteins can be evidenced by fluorescence.
Said applications have recourse to devices using conventional optical means with spectre separation filters.
Said filters have the disadvantage of requiring costly devices that are cumbersome and fragile. The light intensity must be high, which may lead to parasitical fluorescence emissions likely to deteriorate the signal-to-noise ratio and to mask the detection of the relevant signal.